Light Emitting Device

ABSTRACT

An objective is to increase the reliability of a light emitting device structured by combining TFTs and organic light emitting elements. A TFT ( 1201 ) and an organic light emitting element ( 1202 ) are formed on the same substrate ( 1203 ) as structuring elements of a light emitting device ( 1200 ). A first insulating film ( 1205 ) which functions as a blocking layer is formed on the substrate ( 1203 ) side of the TFT ( 1201 ), and a second insulating film ( 1206 ) is formed on the opposite upper layer side as a protective film. In addition, a third insulating film ( 1207 ) which functions as a barrier film is formed on the lower layer side of the organic light emitting element ( 1202 ). The third insulating film ( 1207 ) is formed by an inorganic insulating film such as a silicon nitride film, a silicon oxynitride film, an aluminum nitride film, an aluminum oxide film, or an aluminum oxynitride film. A fourth insulating film ( 1208 ) and a partitioning layer ( 1209 ) formed on the upper layer side of the organic light emitting element ( 1202 ) are formed using similar inorganic insulating films.

This application is a continuation of copending U.S. application Ser.No. 14/816,654, filed on Aug. 3, 2015 which is a continuation of U.S.application Ser. No. 14/341,172, filed on Jul. 25, 2014 (now U.S. Pat.No. 9,099,678 issued Aug. 4, 2015) which is a continuation of U.S.application Ser. No. 11/953,356, filed on Dec. 10, 2007 (U.S. Pat. No.8,790,938 issued Jul. 29, 2014) which is a continuation of U.S.application Ser. No. 11/045,873, filed on Jan. 28, 2005 (now U.S. Pat.No. 7,307,279 issued Dec. 11, 2007) which is a continuation of U.S.application Ser. No. 10/279,635, filed on Oct. 24, 2002 (now U.S. Pat.No. 6,852,997 issued Feb. 8, 2005), which are all incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device prepared with alight emitting element capable of obtaining fluorescence orphosphorescence. In particular, the present invention relates to a lightemitting device in which an active element such as an insulated gatetransistor or a thin film transistor, and a light emitting elementconnected to the active element, are formed in each pixel.

2. Description of the Related Art

Display devices using liquid crystals are structures that typicallyemploy a back light or a front light, and display an image by usinglight from the back light or the front light. Liquid crystal displaydevices are employed as image displaying means in various types ofelectronic devices, but have a structural disadvantage in that theypossess a small angle of view. In contrast, the angle of view is widefor display devices that use a light emitter capable of obtainingelectroluminescence as displaying means, and there is superiorvisibility. Such devices are therefore looked upon as next generationdisplay devices.

The structure of a light emitting element which uses an organic compoundas a light emitter (hereafter referred to as organic light emittingelement) is one in which hole injecting layers, hole transportinglayers, light emitting layers, electron transporting layers, electroninjecting layers, and the like formed by organic compounds are suitablycombined between a cathode and an electrode. Hole injecting layers andhole transporting layers are differentiated and denoted separately here,but they are the same in that their hole transporting characteristics(hole mobility) are very important in particular. For convenience inmaking the distinction, the hole injecting layer is the layer contactingthe anode, and the layer contacting the light emitting layer is referredto as the hole transporting layer. Further, the layer contacting thecathode is referred to as the electron injecting layer, and the layercontacting the other side of the light emitting layer is referred to asthe electron transporting layer. The light emitting layer may also serveas the electron transporting layer, and is referred to as a lightemitting electron transporting layer in that case.

A mechanism in which light is emitted by electroluminescence can beconsidered as a phenomenon in which electrons injected from a cathodeand holes injected from an anode recombine in a layer made from a lightemitter (light emitting layer), forming excitons. Light is emitted whenthe excitons return to a base state. Fluorescence and phosphorescenceexist as types of electroluminescence, and these can be understood aslight emission from singlet state excitation (fluorescence) and lightemission from triplet state excitation (phosphorescence). The brightnessof the emitted light extends from several thousands to several tens ofthousands of cd/m², and therefore it can be considered possible inprinciple to apply this light emission to display devices and the like.However, problems remain in that degradation phenomena exist, and thisimpedes utilization of electroluminescence.

Low molecular weight organic compounds and high molecular weight organiccompounds are known as organic compounds for forming organic lightemitting elements. Examples of low molecular weight organic compoundsinclude: α-NPD (4,4′-bis-[N-(naphthyl)-N-phenyl-amino] biphenyl) andMTDATA (4,4′,4″-tris-(N-3-methylphenyl-N-phenyl-amino) triphenyl amine),both copper phthalocyanine (CuPc) aromatic amine-based materials, usedas hole injecting layers; and a tris-8-quinolinolate aluminum complex(Alq₃) and the like used as light emitting layers. Among high molecularweight organic light emitting materials, polyaniline, polythiophenederivatives (PEDOT), and the like are known.

From the standpoint of material diversity, low molecular weight organiccompounds manufactured by evaporation have striking diversity comparedwith high molecular weight organic materials. However, whichever type isused, organic compounds made purely from only basic structural units arerare, and there are also times when dissimilar bonds and impurities aremixed in during manufacturing processes, and times when variousadditives such as pigments are added. Further, there are materials whichdeteriorate due to moisture, materials which easily oxidize, and thelike among these materials. Moisture, oxygen, and the like can easilymix in from the atmosphere, and therefore it is necessary to exert carein handling.

JP 8-241047 A may be referred to for an example of a combination of athin film transistor (TFT) and a light emitting element. Thispublication discloses a structure in which an organicelectroluminescence layer is formed, through an insulating film madefrom silicon dioxide, on a TFT that uses polycrystalline silicon.Further, a passivation layer, having an end portion which is processedinto a tapered shape on an anode, is positioned in a lower layer side ofthe organic electroluminescence layer. A material having a work functionequal to or lower than 4 eV is selected for a cathode. A material inwhich a metal such as silver or aluminum is alloyed with magnesium isapplied.

Impurities form localized levels within a forbidden band caused byoxygen in semiconductor elements having semiconductor junctions such asdiodes, and the localized levels become a factor in junction leakage andreducing the carrier lifetime, and are known to greatly lower thecharacteristics of the semiconductor elements.

Six types of factors can be considered for organic light emittingelement degradation: (1) chemical change of organic compounds; (2)organic compound melting due to heat generated during driving; (3)dielectric breakdown originating in macro defects; (4) electrodedegradation or electrode and organic compound layer interfacedegradation; (5) degradation caused by instabilities in organic compoundamorphous structure; and (6) irreversible damage due to stress ordistortion caused by the element structure.

The factor (1) above has its origin in chemical change when passingthrough an activation state, chemical change due to certain gasses, orwater vapor, which are corrosive to organic compounds, or the like. Thefactors (2) and (3) result from degradation caused by driving theorganic light emitting elements. Heat generation is inevitable due toelectric current within the elements being converted to Joule heat.Melting occurs if the melting point, or the glass transitiontemperature, of the organic compound is low, and electric fieldsconcentrate in portions where pinholes or cracks exist, causingdielectric breakdown. Degradation advances even at the room temperaturedue to the factors (4) and (5). The factor (4) is known as dark spots,and originates in cathode oxidation and reactions with moisture.Regarding the factor (5), all organic compounds used in the organiclight emitting elements are amorphous materials, and crystallize due toheat emission when stored over a long period of time or are aged, and itcan be thought that almost none are capable of stably preserving theiramorphous structure. Further, irregularities such as film cracking andfracture due to distortion generated by a difference in the thermalexpansion coefficient of structural materials leads to the factor (6).In addition, progressive irregularities such as dark spots also aregenerated in those portions.

Dark spots are suppressed considerably by raising the level of a sealingtechnique used, but actual degradation is generated by a combination ofthe aforementioned factors, and it is difficult to prevent. A method ofsealing organic light emitting elements formed on a substrate by using asealing material, and forming a drying agent such as barium oxide in thesealed space has been devised as a typical sealing technique.

It is known that organic compounds form double bonds due tophoto-deterioration, changing into structures containing oxygen (such as—OH, —OOH, >C═O, —COOH). It can therefore be thought that the bondingstate changes, and degradation proceeds, for cases in which the organiccompounds are placed within an atmosphere containing oxygen, or forcases in which oxygen and moisture are contained within the organiccompounds as impurities.

FIG. 17 is a graph showing the distribution in the depth direction ofoxygen (O), nitrogen (N), hydrogen (H), silicon (Si), and copper (Cu) inan organic light emitting element as measured by secondary ion massspectroscopy (SIMS). The structure of a sample used in the measurementis as follows: a tris-8-quinolinolate aluminum complex (Alq₃)/acarbazole-based material (Ir(ppy)₃+CBP)/copper phthalocyanine (CuPc)/aconductive oxide material (ITO)/a glass substrate. As shown by thechemical formula in FIG. 18B, Alq₃ contains oxygen within its molecules.

On the other hand, the structures shown in the chemical formulae in FIG.18C and FIG. 18A for (Ir(ppy)₃+CBP) and CuPc do not contain oxygenwithin their molecules.

The highest occupied molecular orbital (HOMO) degenerates, and thereforeoxygen molecules are triplet state specific molecules at a base state.An excitation process from a triplet to a singlet normally becomes aforbidden transition (spin forbidden), and thus difficult to occur.Singlet state oxygen molecules therefore do not develop. However, iftriplet state excitation state molecules (³M*) having a higher energystate than that for singlet excitation exist in the periphery of theoxygen molecules, then an energy transfer like that shown below occurs,and this can lead to a reaction in which singlet state oxygen moleculesdevelop.

It is said that 75% of the molecular excitation states in the lightemitting layer of an organic light emitting element are triplet states.Singlet state oxygen molecules can therefore be generated by the energytransfer of FIG. 19 for cases in which oxygen molecules are mixed insidethe organic light emitting element. Singlet excitation state oxygenmolecules have ionic qualities (electric charge polarization), andtherefore the possibility of a reaction with charge polarization thatdevelops in the organic compound can be considered.

For example, methyl groups in vasocuproin (hereinafter, referred to asBCP) are electron donators, and therefore carbon bonded directly toconjugate rings is charged positively. Singlet oxygen having ionicqualities reacts as shown in FIG. 18D if there is positively chargedoxygen, and there is a possibility that carboxylic acid and water areformed as shown in FIG. 18E. As a result, it is expected that theelectron transporting characteristics become deteriorated.

On the other hand, TFTs using a semiconductor as an active layer aredamaged by alkaline metals and alkaline earth metals, which are used ascathode materials in organic light emitting elements. That is, mobileions in these materials get mixed into a gate insulating film or withinan active layer, and switching operations thus become impossible. Insemiconductor manufacturing processes, it is necessary to reduce theconcentration of these metallic impurities to be equal to or less than10⁹ atoms/cm².

SUMMARY OF THE INVENTION

The present invention has been made in view of the aforementionedproblems, and an object of the present invention is to increase thereliability of a light emitting device structured by a combination ofTFTs and organic light emitting elements.

In order to prevent light emitting device deterioration, the presentinvention provides a structure in which: impurities containing oxygen,such as oxygen and moisture, contained within organic compounds formingorganic light emitting elements are reduced; the incursion of moistureand oxygen from the outside is prevented; and a structural material, inwhich these impurities surround an organic compound layer, becomes adiffusion source, and contamination does not occur. Of course this ismade into a structure in which moisture and oxygen from the outside donot penetrate. Oxygen, moisture, and the like are contained as organiccompound structural elements, and the term “impurity” with respect toorganic compounds as used by the present invention denotes exogenousimpurities not contained in the original molecular structure. Theseimpurities are assumed to exist within the organic compounds in anatomic state, a molecular state, as free radicals, and as oligomers.

In addition, the present invention is characterized by having astructure for preventing alkaline metals and alkaline earth metals, suchas sodium, lithium, and magnesium, from contaminating a TFT of an activematrix drive light emitting device, causing the threshold value voltageto fluctuate, and the like.

The present invention removes impurities, reducing the impurityconcentration contained in layers made from organic compounds used informing an organic light emitting element, such as hole injectinglayers, hole transporting layers, light emitting layers, electrontransporting layers, and electron injecting layers, to an averageconcentration equal to or less than 5×10¹⁹/cm², preferably equal to orless than 1×10¹⁹/cm². In particular, it is necessary to reduce theoxygen concentration in the light emitting layer and in the vicinity ofthe light emitting layer. If a phthalocyanine-based or aromatic-basedamine hole injecting layer or hole transporting layer is used, then acarbazole-based light emitting layer or the like will be included in theorganic compound layer.

If the organic light emitting element luminesces at a brightness of 1000Cd/cm², when converted to photons this will correspond to an emissionamount of 10¹⁶/sec·cm². If the quantum efficiency of the light emittinglayer is then assumed to be 1%, then the necessary electric currentdensity demanded is 100 mA/cm². In order to obtain good characteristicsfor an element in which this level of electric current flows, it isnecessary that the defect level density be equal to or less than10¹⁶/cm³ in accordance with an empirical rule based on a semiconductorelement such as a photovoltaic cell or a photodiode using an amorphoussemiconductor. In order to achieve this value, it is necessary that theconcentration of damaging impurity elements which form defect levels beequal to or less than 5×10¹⁹/cm², preferably equal to or less than1×10¹⁹/cm², as stated above.

With an active matrix driving method in which a pixel portion is formedby organic light emitting elements, and each pixel of the pixel portionis controlled by an active element, the structure is such that TFTshaving a semiconductor film, a gate insulating film, and a gateelectrode are formed on a substrate, and the organic light emittingelements are formed on the upper layer of the TFTs. Glass substrates aretypical examples of the substrates used, and very small amounts ofalkaline metals are contained in barium borosilicate glass andaluminosilicate glass. The semiconductor film is covered by siliconnitride and silicon oxynitride in order to prevent contamination byalkaline metals from the glass substrate on the lower layer side and theorganic light emitting element on the upper layer side.

On the other hand, it is preferable that the organic light emittingelements are formed on a leveled surface, and therefore they are formedon a leveling film made from an organic resin material such as polyimideor acrylic. However, these types of organic resin materials arehygroscopic. The organic light emitting elements degrade due to oxygenand moisture, and therefore are covered by an inorganic insulating filmselected from the group of gas barrier materials consisting of siliconnitride, silicon oxynitride, diamond like carbon (DLC), carbon nitride(CN), aluminum nitride, aluminum oxide, and aluminum oxynitride. Theseinorganic insulating films are also effective in preventing thediffusion of alkaline metals or alkaline earth metals, applied ascathode materials, to the TFT side. Further, a partitioning layer formedin the pixel portion is formed by using the same material.

FIG. 10 is a diagram for explaining the concept of an active matrixdrive light emitting device of the present invention. A TFT 1201 and anorganic light emitting element 1202 are formed on the same substrate1203 as structuring elements of a light emitting device 1200. Thestructuring elements of the TFT 1201 are a semiconductor film, a gateinsulating film, a gate electrode, and the like. Silicon, hydrogen,oxygen, and nitrogen are contained within the structuring elements, andmetals and the like are used in forming the gate electrode. On the otherhand, alkaline metals such as lithium and alkaline earth metals arecontained in the organic light emitting element 1202 in addition to themain organic compound material structuring element carbon.

A first insulating film 1205 is formed on the lower layer side of theTFT 1201 (the substrate 1203 side) as a blocking layer. A hydrogencontaining silicon nitride film, a hydrogen containing siliconoxynitride film, or the like is applied as the first insulating film1205. A second insulating film 1206 is formed on the opposite upperlayer side as a protective film. A hydrogen containing silicon nitridefilm, a hydrogen containing silicon oxynitride film, or the like is alsoapplied as the second insulating film 1206.

A third insulating film 1207 is formed as a barrier film on the lowerlayer side of the organic light emitting element 1202. An inorganicinsulating film such as a silicon nitride film, a silicon oxynitridefilm, aluminum nitride, aluminum oxide, or aluminum oxynitride is formedas the third insulating film 1207. It is preferable to reduce theconcentration of hydrogen contained within the film to be equal to orless than 1 atomic % in order to form these films densely. A fourthinsulating film 1208 and a partitioning layer 1209 formed on the upperlayer side of the organic light emitting element 1202 are formed usingsimilar organic insulating films.

An organic resin interlayer insulating film 1204 is formed between thesecond insulating film 1206 and the third insulating film 1207, unifyingthe three films. Alkaline metals, the most disliked by the TFT 1201, areshielded by the first insulating film 1205 and the second insulatingfilm 1206. Further, these films become sources for supplying hydrogenwhich compensates defects in the semiconductor film that is a TFTstructural material. On the other hand, the organic light emittingelement 1202 most dislikes oxygen and moisture, and the third insulatingfilm 1207, the fourth insulating film 1208, and the partitioning layer1209 are formed with the objective of shielding the organic lightemitting element 1202 from oxygen and moisture. Furthermore, these filmsalso function to prevent alkaline metals and alkaline earth metals inthe organic light emitting element 1202 from diffusing to the outside.

According to a structure of the present invention, a light emittingdevice comprises: a first insulating film and a second insulating filmformed by silicon nitride or silicon oxynitride; a semiconductor layer,a gate insulating film, and a gate electrode formed between the firstinsulating film and the second insulating film; a third insulating filmand a fourth insulating film formed by an inorganic insulating materialmade from a nitride; a partitioning layer formed by an inorganicinsulating material made from a nitride; an organic compound layerformed surrounded by the third insulating film, the fourth insulatingfilm, and the partitioning layer; and a cathode formed contacting theorganic compound layer.

Further, according to another structure of the present invention, alight emitting device comprises: a first insulating film and a secondinsulating film formed by silicon nitride or silicon oxynitride; asemiconductor layer of a thin film transistor, a gate insulating film,and a gate electrode formed between the first insulating film and thesecond insulating film; a third insulating film and a fourth insulatingfilm formed by an inorganic insulating material made from a nitride; apartitioning layer formed by an inorganic insulating material made froma nitride; an organic compound layer of an organic light emittingelement formed surrounded by the third insulating film, the fourthinsulating film, and the partitioning layer; and a cathode formedcontacting the organic compound layer.

The first insulating film to the fourth insulating film, and thepartitioning layer in the above structure are not in particular limitedin their manufacturing method. However, a particularly preferableembodiment is to form the first insulating film and the secondinsulating film by using a chemical vapor phase growth method such asplasma CVD, and to for the third insulating film, the fourth insulatingfilm, and the partitioning layer using dense films having good adhesionproperties by using a physical film formation method such as sputtering.In particular, inorganic insulating films formed by high frequencysputtering are suitable. Specifically, silicon nitride manufactured byhigh frequency sputtering using a silicon as a target is suitable. It ispreferable that the amount of oxygen and hydrogen contained be reducedto be equal to or less than 10 atomic %, more preferably equal to orless than 1 atomic %, in order to increase the blocking characteristicsat this point. Further, aluminum nitride and aluminum oxynitride canalso be applied as other materials.

An organic resin interlayer insulating film is formed between the secondinsulating film and the third insulating film in the above structure ofthe present invention, and the interlayer insulating film applies astructure that is used as a leveling film.

In order to give a light emitting device thus structured by combiningTFTs and organic light emitting elements repulsive qualities withrespect to impurity contaminants, the light emitting device is formed byingeniously combining insulating films having blocking characteristicswith respect to oxygen and moisture, thus preventing deterioration dueto the mutual contamination of impurities.

Note that the term light emitting device as used in this specificationindicates general devices using the aforementioned light emitters.Further, modules in which a TAB (tape automated bonding) tape or a TCP(tape carrier package) is attached to an element having a layercontaining a light emitter between an anode and a cathode (hereafterreferred to as a light emitting element), modules in which a printedcircuit board is formed at the end of a TAB tape or a TCP, and modulesin which an IC is mounted by a COG (chip on glass) method to a substrateon which a light emitting element is formed are all included in thecategory of light emitting devices. Furthermore, the concentration ofoxygen as an impurity element as used in this specification indicatesthe lowest concentration as measured by secondary ion mass spectroscopy(SIMS).

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram for explaining the structure of a manufacturingapparatus of the present invention;

FIG. 2 is a diagram for explaining the structure of a film formationapparatus of the present invention;

FIG. 3 is SIMS (secondary ion mass spectroscopy) measurement data for asilicon nitride film;

FIG. 4 is a transmittivity spectrum of a silicon nitride film formed byhigh frequency sputtering using silicon as a target and only nitrogengas;

FIGS. 5A to 5C are diagrams for explaining the structure of a lightemitting element;

FIG. 6 is a partial cross sectional diagram for explaining the structureof a light emitting device prepared with a pixel portion and a drivercircuit portion;

FIG. 7 is a partial cross sectional diagram for explaining the structureof a pixel portion of a light emitting device;

FIG. 8 is a cross sectional diagram for explaining the structure of alight emitting device;

FIG. 9 is a perspective diagram for explaining an outer appearance of alight emitting device;

FIG. 10 is a diagram for explaining the concept of a light emittingdevice of the present invention;

FIG. 11 is FT-IR measurement data of a silicon nitride film;

FIG. 12 is measurement data of the transmittivity of a silicon nitridefilm;

FIG. 13 shows C-V characteristics of a MOS structure before and after aBT stress experiment thereon;

FIGS. 14A and 14B show the C-V characteristics of the MOS structurebefore and after a BT stress experiment thereon;

FIGS. 15A and 15B are diagrams for explaining a MOS structure;

FIG. 16 is a diagram for explaining a sputtering apparatus;

FIG. 17 is a graph showing the distribution in the depth direction ofeach element of a sample having an Alq₃/Ir(ppy)₃+CBP/CuPc/ITO structure,obtained by SIMS measurement;

FIGS. 18A to 18E are chemical formulae of organic compounds;

FIG. 19 is an equation that shows the generation of single state oxygenmolecules by triplet state excitation molecules;

FIG. 20 is a table for formation condition of RFSP-SiN;

FIG. 21 is a table for condition of plasma CVD;

FIG. 22 is a table for comparison of typical parameters of SiN; and

FIG. 23 is a table for parameter of SiN using the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode

An example of an apparatus for manufacturing a light emitting devicecapable of reducing the concentration of impurities contained in organiccompounds, such as oxygen and moisture, is explained using FIG. 1. FIG.1 shows an apparatus for performing film formation and sealing of layersmade from organic compounds and a cathode. A conveyor chamber 101 iscoupled to a loading chamber 104, a preprocessing chamber 105, anintermediate chamber 106, a film formation chamber (A) 107, a filmformation chamber (B) 108, and a film formation chamber (C) 109 throughgates 100 a to 100 f. The preprocessing chamber 105 is provided with theaim of dehydrogenation of processing substrates, degasificationprocessing, and improving surface quality, and heat treatment processingwithin a vacuum or plasma processing using an inert gas becomespossible.

The film formation chamber (A) 107 is a processing chamber mainly forforming a film made from a low molecular weight organic compound byevaporation. The film formation chamber (B) 108 is a processing chamberfor film formation of a cathode containing an alkaline metal byevaporation, and the film formation chamber (C) 109 is a processingchamber for forming silicon nitride films, silicon oxynitride films, andthe like which become passivation films by high frequency sputteringwith a substrate temperature set to the room temperature. The filmformation chamber (A) 107 and the film formation chamber (B) 108 areconnected through the gates 100 h and 100 i to material exchangechambers 112 and 113, respectively, loaded with materials used asevaporation sources. The material exchange chambers 112 and 113 are usedin order to fill the film formation chamber (A) 107 and the filmformation chamber (B) 108 with materials used for evaporation withoutexposure to the atmosphere.

A substrate 103 on which films are to deposited is mounted in the loadchamber 104, and moved to the preprocessing chamber and each filmformation chamber by a conveyor mechanism (A) 102 in the conveyorchamber 101. The loading chamber 104, the conveyor chamber 101, thepreprocessing chamber 105, the intermediate chamber 106, the filmformation chamber (A) 107, the film formation chamber (B) 108, the filmformation chamber (C) 109, and the material exchange chambers 112 and113 are maintained in a reduced pressure state by an evacuating means.The evacuating means performs vacuum evaporation from atmosphericpressure to a pressure on the order of 1 Pa by using an oil free drypump, and greater pressure reductions may be achieved by performingvacuum evacuation using a turbo molecular pump or a compound molecularpump. A cryo-pump may also be established in the film formation chambersin order to remove moisture. Back diffusion of oil vapor from theevacuating means is thus prevented, and the purity of organic compoundlayers is increased.

Inner wall surfaces of the vacuum exhausted chambers undergo specularprocessing by electrolytic polishing, to decrease the surface area,thereby preventing gas emission. Stainless steel or aluminum is used asthe inner wall material. It is preferable to place heaters on theoutside of the film formation chambers, and to perform baking, with agoal of reducing gas emission from the inner walls. Gas emission can begreatly reduced by the baking process. In addition, cooling using arefrigerant may also be performed during evaporation in order to preventimpurity contamination due to gas emission. A vacuum of up to 1×10⁻⁶ Pacan thus be achieved.

The intermediate chamber 106 is connected to an application chamber 110provided with a spinner 111 through the gate 100 g. The applicationchamber 110 is a processing chamber mainly for forming films of organicmaterials made from high molecular weight materials spin coating, andprocessing is performed under atmospheric pressure. Therefore, thesubstrate is carried in and out of the application chamber 110 throughthe intermediate chamber 106, and this is performed by regulating thepressure to be the same as that of the chamber to which the substrate isbeing moved. High molecular weight organic materials to be supplied tothe application chamber are purified by dialysis, electrodialysis, orhigh speed liquid chromatography and then supplied. Purification isperformed at a supply port.

Gas emission processing performed by heat treatment, and surfaceprocessing performed by using an argon plasma are conducted in thepreprocessing chamber 105 as preprocesses for the substrate to beintroduced to the film formation chambers to sufficiently reduceimpurities emitted from the substrate. The impurities emitted from thesubstrate are gaseous components, moisture, organics, and the likeadsorbed to the surface of the substrate. Contamination is reduced byheating the substrate in the preprocessing chamber 105, performingdegasification processing, or by performing plasma processing toincrease the density of the surface. Nitrogen gas and argon gasintroduced to reaction chambers are purified by a purifying means usinga gettering material.

Evaporation is a resistive heating method, and a Knudsen cell may alsobe used in order to control temperature and the amount of evaporationwith high precision. Materials used for evaporation are introduced fromdedicated material exchange chambers incidental to the reactionchambers. Exposure of the reaction chambers to the atmosphere can thusbe avoided as much as possible. Various gasses such as moisture areadsorbed to the inner walls by exposing the film formation chambers tothe atmosphere, and these gasses are re-emitted due to vacuumexhaustion. The time required until emission of the adsorbed gasses isfinished and the vacuum level stabilizes at an equilibrium value is fromseveral hours to several hundreds of hours. An effective countermeasureis to reduce the time by baking the walls of the film formationchambers. However, this is not an effective technique when there isrepeated exposure to the atmosphere, and therefore it is preferable toprovide a dedicated material exchange chamber as shown in FIG. 1. Theevaporation source is mainly an organic material, and purification isperformed within a reaction chamber by sublimation before performingevaporation. Further, purification may also be performed by using a zonemelting method.

On the other hand, a sealing chamber 115 delimited by the loadingchamber 104 seals the substrate, after processing up through cathodeformation is completed, by using a sealing material without exposure tothe atmosphere. An ultraviolet light irradiation mechanism 116 is usedfor cases in which the sealing material is hardened by an ultravioletsetting resin. A conveyor mechanism (B) 118 is provided in a deliverychamber 117, and the substrate subjected to sealing in the sealingchamber 115 is stored in the delivery chamber 117.

FIG. 2 is a diagram for explaining the detailed structure of theconveyor chamber 101 the preprocessing chamber 105 and the filmformation chamber (A) 107. The conveyor mechanism 102 is provided in theconveyor chamber 101. The exhausting means of the conveyor chamber 101is performed by a compound molecular pump or a turbo molecular pump 207a and a dry pump 208 a. The preprocessing chamber 105 and the filmformation chamber 107 are coupled to the conveyor chamber 101 by thegates 100 b and 100 d, respectively. An emission electrode 201 and ahigh frequency electric power source 202 connected to the emissionelectrode 201 are provided in the preprocessing chamber 105, and thesubstrate 103 is held to an opposing electrode provided to a substrateheating means 214. Impurities such as moisture adsorbed onto thesubstrate 103 or onto structures on the substrate 103 can be desorbed byperforming heat treatment under a vacuum or under a reduced pressure toa temperature on the order of 50 to 120° C. using the substrate heatingmeans 214. A gas introducing means connected to the preprocessingchamber 105 is made from a purifier 203 having a cylinder 216 a, a flowregulator 216 b, a gettering material, and the like.

Surface processing using a plasma is performed by purifying an inert gassuch as helium, argon, krypton, or neon, or a combined gas of an inertgas and hydrogen, using the purifier 203, applying high frequencyelectric power, and exposing the substrate within the plasma atmosphere.It is preferable that the purity of the gas used be such that theconcentration of CH₄, CO, CO₂, H₂O, and O₂ each be equal to or less than2 ppm, more preferably equal to or less than 1 ppm.

The evacuating means performs evacuation by using a turbo molecular pump207 b or a dry pump 208 b. Pressure control within the preprocessingchamber 105 during surface processing is performed by controlling theevacuation speed using a control valve prepared in the evacuating means.

The film formation chamber 107 is prepared with an evaporation source211, an adsorption plate 212, a shutter 218, and a shadow mask 217. Ashutter 218 is an open and close type, and is open during evaporation.The evaporation source 211 and the adsorption plate 212 are forcontrolling temperature, and are connected to heating means 213 d and213 c, respectively. An evacuation system includes the turbo molecularpump 207 c and the dry pump 208 c, and, a cryo-pump 209 is further addedmaking it possible to remove moisture remaining within the filmformation chamber. Baking processing is performed and it becomespossible to reduce the amount of gas emitted from the walls within thereaction chamber. Baking is performed by vacuum evacuation using theevacuation system, to which the turbo molecular pump and the cryo-pumpare connected, while heating the film formation chamber to a temperatureon the order of about 50 to 120° C. It is possible to perform vacuumevaporation to a pressure on the order of 1×10⁻⁶ Pa by cooling thereaction chamber to the room temperature or to a temperature on theorder of liquid nitrogen by using a refrigerant.

Evaporation sources 210 and 219 are provided in the material exchangechamber 112 delimited by the gate 100 h, and this becomes a mechanism inwhich temperature is controlled by heating means 213 a and 213 b. Aturbo molecular pump 207 d and a dry pump 208 d are used in theevacuation system. The evaporation source 219 is moveable between thematerial exchange chamber 112 and the film formation chamber 107, and isused as a means for performing purification of the evaporation materialto be supplied.

There are no limitations placed on the method of purifying theevaporation materials, but it is preferable to employ a sublimationpurification method when performing purification within themanufacturing apparatus. A zone purification method may also beperformed, or course.

An organic light emitting element manufactured by using themanufacturing apparatus explained with reference to FIG. 1 and FIG. 2 isnot limited in structure. Organic light emitting elements are formed byforming a layer made from organic compounds between an anode composed ofa transparent conductive film and a cathode which contains an alkalinemetal. The layer made from organic compounds may be formed by a singlelayer or a lamination of a plurality of layers. A distinction is madebetween each layer based upon the aim and function of the layer, and thelayers are referred to as hole injecting layers, hole transportinglayers, light emitting layers, electron transporting layers, electroninjecting layers, and the like. It is possible to form these layers byusing low molecular weight organic compound materials, intermediatemolecular weight organic compound materials, high molecular weightorganic compound materials, or a mixture of suitable amounts of thesematerials. Further, a mixed layer in which an electron transportingmaterial and a hole transporting material are suitably mixed may also beformed, as may a mixed junction in which a mixed region is formed injunction boundaries of an electron transporting material and a holetransporting material.

Organic compound materials having superior hole transportingcharacteristics are selected for hole injecting layers and holetransporting layers, and typically a phthalocyanine or an aromatic aminematerial is employed. Further, metallic chains and the like havingsuperior electron transporting characteristics are used in electroninjecting layers.

An example of the structure of an organic light emitting element isshown in FIGS. 5A to 5C. FIG. 5A is an example of an organic lightemitting element using low molecular weight organic compounds. An anode300 formed by indium tin oxide (ITO), a hole injecting layer 301 formedby copper phthalocyanine (CuPc), a hole transporting layers 302 and 303formed by MTDATA and α-NPD which are aromatic amine materials, acombination electron injecting and light emitting layer 304 formed bytris-8-quinolinolate aluminum complex (Alq₃), and a cathode 305 madefrom ytterbium (Yb) are laminated. Light emission (fluorescent light) ofAlq₃ is possible from a singlet excitation state. Further, apartitioning layer 330 covering an edge portion of the anode 300 isformed by an inorganic insulating material such as silicon nitride.

It is preferable to use light emission from a triplet excitation state(phosphorescence) in order to increase brightness. An example of thattype of element structure is shown in FIG. 5B. An anode 310 formed byITO, a hole injecting layer 311 formed by CuPc which is a phthalocyaninematerial, a hole transporting layer 312 formed by α-NPD which is anaromatic amine material, and a light emitting layer 313 formed on thehole transporting layer 312 using CBP+Ir(ppy)₃ which is a carbazole, areformed. In addition, the structure has a hole blocking layer 314 formedby using vasocuproin (BCP), an electron injecting layer 315 formed fromAlq₃, and a cathode 316 containing an alkaline metal such as ytterbium(Yb) or lithium. Furthermore, a blocking layer 331 covering an edgeportion of an anode 310 is formed by using an inorganic insulatingmaterial such as silicon nitride.

The above-mentioned two structures are examples of using low molecularweight organic compounds. Organic light emitting elements can also beachieved by combining high molecular weight organic compounds and lowmolecular weight organic compounds. FIG. 5C is an example thereof, andan anode 320 is formed by ITO, on which a hole injecting layer 321 isformed by the high molecular weight organic compound polythiophenederivative (PEDOT), a hole transporting layer 322 is formed by α-NPD, alight emitting layer 323 is formed by CBP+Ir(ppy)₃, a hole blockinglayer 324 is formed by BCP, an electron injecting layer 325 is formed byAlq₃, and a cathode 326 containing an alkaline metal such as ytterbium(Yb) or lithium is formed. The hole injecting characteristics of thehole injecting layer are improved by changing to PEDOT, and the lightemitting efficiency can be increased. Further, a blocking layer 332covering an edge portion of an anode 320 is formed using an inorganicinsulating material such as silicon nitride.

The carbazole CBP+Ir(ppy)₃ used as the light emitting layer is anorganic compound capable of obtaining light emission from a tripletexcitation state (phosphorescence). The organic compounds discussed inthe following papers can be given as typical triplet compound materials.(1) T. Tsutsui, C. Adachi, S. Saito, Photochemical Processes inOrganized Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo,1991) p. 437. (2) M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S.Sibley, M. E. Thompson, S. R. Forrest, Nature 395 (1998) p. 151. In thisessay, the organic compound represented by the following formula isdisclosed. (3) M. A. Baldo, S. Lamansky, P. E. Burrrows, M. E. Thompson,S. R. Forrest, Appl. Phys. Lett, 75 (1999) p. 4. (4) T. Tsutsui, M.-J.Yang, M. Yahiro, K. Nakamura, T. Watanabe, T. Tsuji, Y. Fukuda, T.Wakimoto, S. Mayaguchi, Jpn. Appl. Phys., 38 (12B) (1999) L1502.

Whichever type of material is used, light emission from a tripletexcitation state (phosphorescence) has higher light emission efficiencythan light emitted from a singlet excitation state (fluorescence), andit is thus possible to reduce the operating voltage (the voltagerequired in order to make the organic light emitting element emit light)and obtain the same brightness in the emitted light.

The phthalocyanine CuPc, the aromatic amine α-NPD, MTDATA, the carbazoleCBP and the like are organic compounds which do not contain oxygen. Achange in bonding state occurs like that explained using the chemicalequations Chem. 4 and Chem. 5 due to mixture of oxygen or moisture intothese organic compounds, and the hole transporting characteristics andthe light emitting characteristics are degraded. The manufacturingapparatus explained by using FIG. 1 and FIG. 2 is employed in forminglayers of organic compounds described above. The concentration of oxygenwithin the light emitting element can thus be reduced to be equal to orless than 1×10¹⁹/cm³. In addition, the concentration of oxygen can alsobe reduced to be equal to or less than 1×10¹⁹/cm³ in hole injectinglayers and hole transporting layers in organic light emitting elementshaving a phthalocyanine or an aromatic amine hole injecting layer orhole transporting layer, and a carbazole light emitting layer.

Note that, although not shown in FIGS. 5A to 5C, there are interfacesbetween the materials used to form the layers such as the light emittinglayer, the hole injecting layer, the electron injecting layer, the holetransporting layer, and the electron transporting layer, and anembodiment can be made in which the materials from a plurality of layersare mixed. High molecular compounds such as polyparaphenylene vinylenes,polyparaphenylenes, polythiofenes, polyfluorenes, and the like may alsobe used for the organic compound layers. In addition to the embodimentin which each layer is formed using an organic compound, inorganiccompounds may also be used for the hole injecting and transportinglayers and the electron injecting and transporting layers. Inorganiccompound materials include diamond like carbon (DLC), carbon nitride,Si, Ge, and oxide and nitrides of these materials. Materials in which P,B, N, or the like is suitably doped may also be used. Further, dioxides,nitrides, and fluorides of alkaline metals or alkaline earth metals maybe used, and chemical compounds and alloys of alkaline metals andalkaline earth metals and at least Zn, Sn, V, Ru, Sm, and In may also beused.

FIG. 6 is an example showing the structure of an active matrix drivelight emitting device. TFTs are formed in a pixel portion and in variouskinds of functional circuits in the periphery of the pixel portion. Itis possible to select amorphous silicon or polycrystalline silicon assemiconductor film materials used in forming channel forming regions ofthe TFTs, and the present invention may employ either material.

A substrate 601 employs a glass substrate or an organic resin substrate.Organic resin materials are light weight compared to glass materials,and are effective in making the light emitting device itself lightweight. Organic resin materials such as polyimide, polyethyleneterephthalate (PET), polyethylene naphthalene (PEN), polyether sulfone(PES) and aramid are materials capable of being applied to manufactureof the light emitting device. Glass substrates are referred to asnon-alkaline glass, and it is preferable to use barium borosilicateglass or aluminum borosilicate glass. A thickness of 0.5 to 1.1 mm isemployed for the glass substrate, and it is necessary to make thethickness small in order to achieve light weight. Further, it ispreferable to use a glass substrate having a low specific gravity of2.37 g/cc in order to achieve even lighter weight.

A state is shown in FIG. 6 in which an n-channel TFT 652 and a p-channelTFT 653 are formed in a driver circuit portion 650, and a switching TFT654 and an electric current control TFT 655 are formed in a pixelportion 651. These TFTs are formed using semiconductor films 603 to 606,a gate insulating film 607, gate electrodes 608 to 611, and the like ona first insulating film 602 made from silicon oxide, silicon nitride, ora silicon oxynitride laminate.

A second insulating film 618 made from silicon nitride or siliconoxynitride is formed on the gate electrodes, and is used as a protectivefilm. In addition, an organic insulating film 619 made from polyimide oracrylic is formed as a leveling film. This organic insulating film hashygroscopic characteristics, and possesses property of occludingmoisture. Oxygen is supplied to the organic compounds if moisture isremitted, and becomes a cause of degradation of the organic lightemitting element. A third insulating film 620 formed by an inorganicinsulating material selected from silicon nitride, silicon oxynitride,aluminum oxynitride, aluminum nitride, and the like is therefore formedon the organic insulating film 619 in order to prevent moistureocclusion and reemission.

The circuit structure of the driver circuit portion 650 differs betweena gate signal line side driver circuit and a data signal line sidedriver circuit, but this difference is omitted here. Wirings 612 and 613are connected to the n-channel TFT 652 and the p-channel TFT 653, and itis possible to form a shift register, a latching circuit, a buffercircuit, and the like by using these TFTs.

A data wiring 614 is connected to a source side of the switching TFT654, and a drain side wiring 615 is connected to the gate electrode 611of the electric current control TFT 655 in the pixel portion 651.Further, a source side of the electric current control TFT 655 isconnected to an electric current supply wiring 617, and a drain sideelectrode 616 is wired such that it is connected to an anode of anorganic light emitting element.

An organic light emitting element 656 is made from an anode 621 formedon the third insulating film 620 by ITO (indium tin oxide), an organiccompound layer 623 containing a hole injecting layer, a holetransporting layer, a light emitting layer, and the like, and a cathode624 formed by using a material containing an alkaline metal or analkaline earth metal such as MgAg, LiF, crystalline semiconductor film,BaF, or CaF. The structure of the organic light emitting element may bearbitrary, and the structure shown in FIG. 5 can be employed.

A partitioning layer 622 is formed by a nitride inorganic insulatingmaterial. Specifically, the partitioning layer 622 is formed by aninorganic insulating material selected from silicon nitride, aluminumnitride, and aluminum oxynitride. The partitioning layer 622 is formedat a thickness on the order of 0.1 to 1 μm, and is formed so that anedge portion overlapping with the anode 621 has a tapered shape. Thepartitioning layer 622 is formed so as to cover the upper and sidesurfaces of a photo resist 626 remaining on the wirings 612 to 617.Further, although not shown in the figure, an insulating film having athickness of 0.5 to 5 mm, an order at which a tunneling electric currentwill flow, may also be formed in the interface between the anode 621 andthe organic compound layer 623. The insulating film is effective inpreventing short circuits caused by roughness in the surface of theanode, and in deterring alkaline metals and the like used in the cathodefrom diffusing to the lower layer side.

The cathode 624 of the organic light emitting element uses a materialcontaining magnesium (Mg), lithium (Li) or calcium (Ca), each having asmall work function. An MgAg (a material in which Mg and Ag are mixed ata ratio of Mg::Ag=10::1) electrode is preferably used. MgAgAlelectrodes, LiAl electrodes, and LiFAl electrodes can be given as otherexamples. In addition, a fourth insulating film 625 is formed on thecathode 624 by using an inorganic insulating material selected fromsilicon nitride, DLC, aluminum oxynitride, aluminum oxide, aluminumnitride, and the like. DLC films are known to have high gas barriercharacteristics to oxygen, CO, CO₂, H₂O, and the like. It is preferableto form the fourth insulating film 625 in succession, without exposureto the atmosphere, after forming the cathode 624. A silicon nitridepartitioning layer may also be used as a lower layer of the fourthinsulating film 625. This is because the state of the interface betweenthe cathode 624 and the organic compound layer 623 is known to exert agreat influence on the light emitting efficiency of the organic lightemitting element.

The switching TFT 654 uses a multi-gate structure in FIG. 6, and a lowconcentration drain (LDD) overlapping with the gate electrode is formedin the electric current control TFT 655. TFTs using polycrystallinesilicon performs a high operating speed, and therefore degradation dueto hot carrier injection and the like occurs easily. Therefore, as shownin FIG. 6, the formation of TFTs having different structures,corresponding to their function within a pixel (a switching TFT having asufficiently low off current, and an electric current control TFT whichis strong with respect to hot carrier injection), is therefore extremelyeffective in manufacturing a display device having high reliability andcapable of good image display (high operating efficiency).

The first insulating film 602 is formed on the lower side of thesemiconductor film which forms the TFTs 654 and 655, as shown in FIG. 6.The second insulating film 618 is formed on the opposite upper layerside. On the other hand, the third insulating film 620 is formed on thelower layer side of the organic light emitting element 656, and further,the partitioning layer 622 is formed therebetween. These films are allformed by inorganic insulating materials. The organic light emittingelement 656 is formed within these films, sandwiched by the thirdinsulating film 620, the fourth insulating film 625, and thepartitioning layer 622, and is unified with these films.

The substrate 601 and the organic light emitting element 656 can beconsidered as sources of contamination of alkaline metal, such assodium, with respect to the TFTs 654 and 655, but the contamination canbe prevented by surrounding the TFTs using the first insulating film 602and the second insulating film 618. On the other hand, the organic lightemitting element 656 most dislikes oxygen and moisture, and thereforethe third insulating film 620, the fourth insulating film 625, and thepartitioning layer 622 are formed by inorganic insulating materials.These films also function so that alkaline metal elements in the organiclight emitting element 656 do not go outside.

In particular, one example of a material appropriate for use in formingthe third insulating film 620, the partitioning layer 622, and thefourth insulating film 625 is a silicon nitride film manufactured bysputtering using silicon as a target. Specifically, the silicon nitridefilm has extremely compact film qualities when formed by high frequencysputtering, and is formed by the process conditions shown in FIG. 20(typical examples are also included in FIG. 20). Note that the term“RFSP-SiN” within FIG. 20 indicates a silicon nitride film formed byhigh frequency sputtering. Further the term “T/S” denotes the distancebetween the target and the substrate.

Ar is used as the sputtering gas, and is introduced so as to be blown onthe rear surface of the substrate as a gas for heating the substrate. N₂is finally mixed in, and contributes to sputtering. Further, the filmformation conditions shown in FIG. 20 are typical conditions, and thefilm formation conditions are not limited by the values shown in FIG.20. The conditions may be suitably changed by an operator provided thatthe characteristic parameters of the formed SiN film fall within thecharacteristic pattern range to be shown later in FIG. 23.

A schematic diagram of a sputtering apparatus used in forming thesilicon nitride film by high frequency sputtering is shown in FIG. 16.Reference numeral 30 in FIG. 16 denotes a chamber wall, referencenumeral 31 denotes a moveable magnet for forming an electric field,reference numeral 32 denotes a single crystal silicon target, referencenumeral 33 denotes a protective shutter, reference numeral 34 denotes asubstrate to be processed, reference numerals 36 a and 36 b denoteheaters, reference numeral 37 denotes a substrate fastening mechanism,reference numeral 38 denotes a shield, and reference numeral 39 denotesa valve (conductance valve or main valve). Further, gas introductionpipes 40 and 41 provided in the chamber wall 30 are pipes forintroducing N₂ (or a mixed gas of N₂ and an inert gas) and an inert gas,respectively.

Further, film formation conditions for a silicon nitride film formed byconventional plasma CVD are shown in FIG. 21. Note that the term“PCVD-SiN” within FIG. 21 indicates a silicon nitride film formed byplasma sputtering.

Next, typical characteristic values (characteristic parameters) ofsilicon nitride films formed under the film formation conditions of FIG.20 and silicon nitride films formed by the film formation conditions ofFIG. 21 are compared, and the results are shown in FIG. 22. Note thatthe difference between “RFSP-SiN (No. 1)” and “RFSP-SiN (No. 2)” is adifference due to the film formation apparatus, and their function assilicon nitride films used as barrier films of the present invention isnot lost. Furthermore, although the reference symbol sign of thenumerical values for internal stress change between compressive stressand tensile stress, only absolute values are used here.

Common characteristic points between the RFSP-SiN (No. 1) and theRFSP-SiN (No. 20) are that the etching speed is slow compared to thePCVD-SiN film (etching speed when etching at 20° C. using LAL500;hereafter the same), and that the hydrogen concentration is low. Notethat the term “LAL500” denotes the product “LAL 500 SA bufferedhydrofluoric acid” manufactured by Hashimoto Chemical KK, and is anaqueous solution of NH₄HF₂ (7.13%) and NH₄F (15.4%). Further, theinternal stress becomes a smaller value than that for the siliconnitride film formed by plasma CVD when comparing absolute values.

The applicants of the present invention have compiled in FIG. 23parameters for various physical properties of silicon nitride filmsformed by the film formation conditions of FIG. 20.

Further, results of investigating the silicon nitride films by SIMS(secondary ion mass spectroscopy) are shown in FIG. 3, and FT-IR resultsare shown in FIG. 11, and the transmittivity of the silicon nitridefilms is shown in FIG. 12. Note that the silicon nitride films formedunder the film formation conditions of FIG. 21 are also shown in FIG.12. Regarding transmittivity, there is no inferiority compared toconventional PCVD-SiN films.

FIG. 11 shows an infrared absorption spectrum of a silicon nitride film(#001) formed by sputtering using only a nitrogen gas, and applying highfrequency electric power at 13.56 MHz. The main film formationconditions are the use of a 1 to 2 Ω sq. silicon target to which boronis added, the supply of only nitrogen gas, and a high frequency electricpower (13.56 MHz) of 800 W. The target size has a diameter of 152.4 mm.Film formation of 2 to 4 nm/min was obtained under these conditions.

The characteristics of a silicon oxide film (#002) manufactured bysputtering and a silicon nitride film (#003) manufactured by plasma CVDare inputted as comparison data in FIG. 11. The film formationconditions of each film are noted within Table 1, and therefore may bereferred to. The silicon nitride film denoted by sample number #001formed at the room temperature is formed using only nitrogen as asputtering gas, and absorption peaks for N—H bonds and Si—H bonds arenot observed. Further, an Si—O absorption peak is also absent in thisfilm. It is understood from these characteristics that the concentrationof oxygen and the concentration of hydrogen within the film are equal toor less than 1 atomic %.

TABLE 1 Sample No. #001 #002 #003 (RF-SP SiN) (RF-SP SiO2) (PCVD SiN)Rotation of  5 None None substrate (rpm) Temperature of Room 150 300substrate (° C.) Temperature Heating gas None O2 = 10 sccm Electricpower of 800 W 3 kW 170 W film formation (RF) Pressure of film 0.4 Pa0.4 Pa 1.2 torr formation Gas flow Ar/O2/N2 = Ar/O2/N2 = SiH4/NH3/N2/H2= (sccm) 0/0/40 35/15/0 30/240/300/60 Film thickness 500 500 500 (nm)

FIG. 4 shows transmittivity for three types of structures on anon-alkaline glass substrate (Corning Corp., substrate #1737): a siliconnitride film, an acrylic resin film, and a laminate of an acrylic resinfilm and a silicon nitride film. A transmittivity equal to or greaterthan 80% was found in visible light. In particular, there is atransmittivity equal to or greater than 80% for a wavelength of 400 nm,thus showing the transparent characteristics of this film. This assumesa state in which the organic insulating film 619 and the thirdinsulating film 620 in FIG. 6 are laminated together, and shows thatthere will be little change in tint, even if light from the organiclight emitting element is emitted toward the glass substrate.

In the silicon nitride film used as a inorganic insulating layer of thepresent invention, a silicon nitride film which satisfies the parametershown in FIG. 4 is desirable. That is, as the inorganic insulatinglayer, it is desirable to satisfy any of (1) using a silicon nitridefilm having an etching rate of 9 nm/min or less (preferably, 0.5 to 3.5nm/min or less), (2) having a hydrogen concentration of 1×10²¹atoms/cm⁻³ or less (preferably, 5×10²⁰ atoms/cm⁻³ or less), (3) having ahydrogen concentration of 1×10²¹ atoms/cm⁻³ or less (preferably, 5×10²⁰atoms/cm⁻³ or less), and an oxygen concentration of 5×10¹⁸ to 5×10²¹atoms/cm⁻³ or less (preferably, 1×10¹⁹ to 1×10²¹ atoms/cm⁻³ or less),(4) having an etching rate of 9 nm/min or less (preferably, 0.5 to 3.5nm/min or less), and a hydrogen concentration of 1×10²¹ atoms/cm³ orless (preferably, 5×10²⁰ atoms/cm⁻³ or less), and (5) having an etchingrate of 9 nm/min or less (preferably, 0.5 to 3.5 nm/min or less), ahydrogen concentration of 1×10²¹ atoms/cm³ or less (preferably, 5×10²⁰atoms/cm⁻³ or less), and an oxygen concentration of 5×10¹⁸ to 5×10²¹atoms/cm⁻³ or less (preferably, 1×10¹⁹ to 1×10²¹ atoms/cm⁻³ or less).

Further, the absolute value of the internal stress may be set equal toor less than 2×10¹⁰ dyn/cm², preferably equal to or less than 5×10⁹dyn/cm², and more preferably equal to or less than 5×10⁸ dyn/cm². Levelgeneration in interfaces with other films can be reduced if the internalstress is made smaller. In addition, film peeling due to internal stresscan be prevented.

Furthermore, the blocking effect against Na, Li, and other elementsresiding in group 1 and group 2 of the periodic table is extremelystrong in the silicon nitride film formed in accordance with the filmformation conditions of FIG. 20 disclosed in this embodiment mode. Thediffusion of these mobile ions and the like can be effectivelysuppressed. For example, a metallic film in which 0.2 to 1.5 wt %(preferably 0.5 to 1.0 wt %) of aluminum is added to lithium ispreferable in its electron injecting characteristics and othercharacteristics when used as a cathode layer in this embodiment mode,although in this case there is concern that the diffusion of lithiumwill adversely affects transistor operation. However, there is completeprotection by the inorganic insulating layers in this embodiment mode,and therefore it is not necessary to worry about the diffusion oflithium in the direction of the transistors.

Data showing this fact is shown in FIGS. 13 to 15B. FIG. 13 is a diagramshowing the change in the C-V characteristics before and after BT stresstests on a MOS structure in which a silicon nitride film formed by thefilm formation conditions of FIG. 21 (PCVD-SiN film) is used as adielectric. The structure of a sample is as shown in FIG. 15A, and thepresence or absence of influence due to lithium diffusion can beascertained by using an Al—Li (aluminum to which lithium is added)electrode in a surface electrode. According to FIG. 13, the C-Vcharacteristics shift greatly due to the BT stress test, and it can beconfirmed that influence due to the diffusion of lithium from thesurface electrode clearly appears.

Next, FIGS. 14A and 14B are C-V characteristics before and after BTstress tests of MOS structures in which silicon nitride films formedunder the film formation conditions of FIG. 20 are used as dielectrics.The difference between FIG. 14A and FIG. 14B is that while an Al—Si(aluminum film to which silicon is added) is used as a surface electrodein FIG. 14A, an Al—Li (aluminum film to which lithium is added) is usedas a surface electrode in FIG. 14B. Note that the results of FIG. 14Bare the results of measurements of the MOS structure shown in FIG. 15B.A thermal oxidation film and a laminate structure is used here in orderto reduce the influence of interface levels between the silicon nitridefilm and the silicon substrate.

Comparing the graphs of FIG. 14A and FIG. 14B, there is almost nodifference in the shift of the C-V characteristics in both graphs beforeand after the BT stress tests, and influence caused by lithium diffusiondoes not appear. That is, it can be confirmed that the silicon nitridefilm formed under the film formation conditions of FIG. 20 functionseffectively as a blocking film.

The inorganic insulating films used in the present invention areextremely dense and have a good blocking effect against the mobileelements Na and Li. The diffusion of outgassing components from theleveling film is therefore suppressed, and the diffusion of Li from theAl—Li electrode and the like is effectively suppressed, and a displaydevice having high reliability can thus be achieved. The applicants ofthe present invention conjecture that the reason for the dense filmformation is that a thin silicon nitride film formed on the surface ofthe single crystal silicon target, and that silicon nitride film islaminated onto the substrate during film formation, and thereforesilicon clusters are difficult to mix into the film. As a result, thefilm becomes dense.

Further, the film is formed by low temperature sputtering on the orderof the room temperature to 200° C. This is more effective than plasmaCVD in that film formation can be performed on resin films, as whenusing the film as a barrier film of the present invention.

Note that the aforementioned silicon nitride film can also be used as apassivation film covering the organic light emitting element, and aportion of the silicon nitride film can be used for cases in which thegate insulating film is formed by a laminate film.

In addition, a successive film formation process can be employed in themethod of manufacturing a light emitting device having a structure likethat shown by FIG. 6 by forming the third insulating film 620 and theanode 621, manufactured by using a transparent conductive film,typically ITO, by sputtering. Sputtering is suitable in forming a densesilicon nitride film or silicon oxynitride film without impartingconspicuous damage to the surface of the organic insulating film 619.

A light emitting device can thus be completed by forming a pixel portionin which TFTs and a light emitting device are combined. This type oflight emitting device can form the driver circuits on the same substrateusing TFTs. By surrounding the semiconductor film, the gate insulatingfilm, and the gate electrodes, which are the main structural elements ofthe TFTs, on their lower layer and upper layer sides by using blockinglayers and protective films made from silicon nitride or siliconoxynitride, a structure will result in which contamination due toalkaline metals and organics can be prevented. On the other hand, theorganic light emitting element contains alkaline metals. A structure inwhich the penetration of oxygen and moisture from the outside isprevented can be obtained by surrounding the organic light emittingelement with a protective film made from silicon nitride, siliconoxynitride, or a DLC film, and a gas partitioning layer made from aninsulating film having silicon nitride or carbon as its mainconstituent.

A technique of completing a light emitting device in which elementshaving different characteristics with respect to impurities arecombined, without mutual interference, is thus provided.

A top gate TFT structure is explained by FIG. 6, but it is alsopossible, of course, to apply bottom gate TFTs and reverse stagger TFTs.Reverse stagger TFTs are applied to a pixel portion 751 in FIG. 7, and aswitching TFT 754 and an electric current control TFT 755 are formed.Gate electrodes 702 and 703, and a wiring 704 are formed on a substrate701 by using molybdenum, tantalum, or the like, and a first insulatingfilm 705 that functions as a gate insulating film is formed thereon.Silicon oxide, silicon nitride, or the like at a thickness of 100 to 200nm is used in forming the first insulating film.

In addition to channel forming regions, source or drain regions and LDDregions are formed in semiconductor films 706 and 707. These regions areformed, and insulating films 708 and 709 are formed in order to protectthe channel forming regions. A second insulating film 710 is formed bysilicon nitride or silicon oxynitride, and is formed so that thesemiconductor film is not contaminated by alkaline metals, organics, andthe like. In addition, a leveling film 711 made from an organic resinmaterial such as polyimide is formed. A third insulating film 712 madefrom silicon nitride or silicon oxide is formed on the leveling film711. Wirings 713 to 716 are formed on the third insulating film 712.

An anode 717 of an organic light emitting element 756 is formed on thethird insulating film 712, and a partitioning layer 718 is formedafterward by using an inorganic insulating material selected from thegroup consisting of silicon nitride, silicon oxynitride, aluminumoxynitride, aluminum oxide, and aluminum nitride. Further, thepartitioning layer 718 is formed covering upper surfaces and sidesurfaces of photoresist 723 which remains on the wirings 713 to 716. Inaddition, the partitioning layer 718 is formed so as to cover edgeportions of the anode 717 and the TFT wirings, and prevents shortcircuits between a cathode and the anode in these portions. Structuresfor an organic compound layer 720, a cathode 721, and a fourthinsulating film are formed similarly to those of FIG. 6, and a fourthinsulating film 722 is formed similarly to the third insulating film712. A light emitting device having reverse stagger TFTs can thus becompleted.

Although only the pixel portion is shown in FIG. 7, driver circuits canalso be formed on the same substrate by using reverse stagger TFTs. Thesemiconductor film, which is the main structural element of the TFTs, issurrounded on its lower layer side and its upper layer side by the firstinsulating film and the second insulating film made from silicon nitrideor silicon oxynitride as shown in FIG. 7, and this is a structure inwhich contamination by alkaline metals and organics is prevented. On theother hand, the organic light emitting element contains alkaline metals,and a structure in which the penetration of oxygen and moisture from theoutside is prevented is obtained from using the third insulating film,the fourth insulating film, and the partitioning layer 718. A techniqueof completing a light emitting device in which elements having differentcharacteristics with respect to impurities are combined, without mutualinterference, can thus be provided by using reverse stagger TFTs.

A structure in which an organic light emitting element is sealed isshown in FIG. 8. A state is shown in FIG. 8 in which an elementsubstrate 401 on which a driver circuit 408 and a pixel portion 409 areformed using TFTs, and a sealing substrate 402 are fixed by a sealingmaterial 405. A protective film 406 is formed by a material selectedfrom the group consisting of silicon nitride films, silicon oxynitridefilms, DLC films, carbon nitride films, aluminum oxide films, aluminumnitride films, and aluminum oxynitride films. Further, a silicon nitridefilm may also be used as a buffer layer below the protective film 406.An organic light emitting element 403 is formed within a sealed regionbetween the element substrate 401 and the sealing substrate 402, and adrying agent may also be placed on the driver circuit 408 or in thevicinity of where the sealing material 405 is formed.

An organic resin material such as polyimide, polyethylene terephthalate(PET), polyethylene naphthalene (PEN) polyether sulfone (PES) and aramidis used for the sealing substrate. A thickness on the order of 30 to 120μm is employed for the sealing substrate, providing flexibility. A DLCfilm is formed as a gas partitioning layer 407 in an edge portion. Notethat the DLC film is not formed on an external input terminal 404. Anepoxy adhesive is used as the sealing material. By forming the gaspartitioning layer 407 along the sealing material 405, and along edgeportions of the element substrate 401 and the sealing substrate 402, thepermeation of water vapor can be prevented. The gas partitioning layer407 is not limited to a DLC film, and can also be formed by materialssimilar to those used for the protective film 406.

FIG. 9 is a diagram showing an external view of this type of displaydevice. Although the direction to which an image is displayed differs inaccordance with the organic light emitting element structure, in thiscase light is emitted in an upward direction, to perform image display.The element substrate 401, on which the driver circuit portion 408 andthe pixel portion 409 are formed by using TFTs, and the sealingsubstrate 402 are bonded by using the sealing material 405 in thestructure shown by FIG. 9. Further, in addition to the driver circuitportion 408, a signal processing circuit 606 for correcting a videosignal and for storing the video signal may also be formed. The inputterminal 404 is formed in an edge of the element substrate 401, and anFPC (flexible printed circuit) is connected to this portion. Terminalsfor inputting an image data signal, various types of timing signals, andelectric power from external circuits are formed in the input terminal404 at a pitch of 500 μm. A connection with the driver circuit portionis made by a wiring 410. Further, an IC chip 411 in which a CPU, memory,and the like are formed may also be mounted on the element substrate 401by using COG (chip on glass) or the like when necessary.

The DLC film is formed in edge portions adjacent to the sealingmaterial, and water vapor, oxygen, and the like from the sealing portionare prevented from penetrating, thus preventing degradation of theorganic light emitting element. The input terminal portion may beomitted and instead, a DLC film may be formed over the entire surfacefor cases in which an organic resin material is used for the elementsubstrate 401 and the sealing substrate 402. The input terminal portionmay be covered in advance by using masking tape of a shadow mask whenforming the DLC film.

The organic light emitting element can thus be sealed, and a lightemitting device can be formed. This becomes a structure in which theTFTs and the organic light emitting elements are surrounded byinsulating films, and impurities from the outside do not penetrate. Inaddition, the element substrate is bonded using a sealing material, andthe airtightness is increased by covering edge portions using DLC.Degradation of the light emitting device can thus be prevented.

As explained above, the concentration of oxygen as an impurity elementin layers made from organic compounds that function as hole injectinglayers, hole transporting layers, light emitting layers, and the like inorganic light emitting elements can be reduced to a level equal to orless than 5×10¹⁹/cm³, preferably equal to or less than 1×10¹⁹/cm³, byusing the present invention. Further, semiconductor films, gateinsulating films, and gate electrodes, which are the main structuralelements of TFTs, are surrounded by inorganic insulating materialsselected from the group consisting of silicon nitride, siliconoxynitride, aluminum oxynitride, aluminum oxide, and aluminum nitridewith the present invention, thus providing a structure in whichcontamination by alkaline metals and organics is prevented. On the otherhand, organic light emitting elements contain alkaline metals, and astructure in which penetration of oxygen and moisture from the outsideis prevented by surrounding the organic light emitting elements using aninorganic insulating material selected from the group consisting ofsilicon nitride, silicon oxynitride, aluminum oxynitride, aluminumoxide, aluminum nitride, DLC, and carbon nitride is achieved. Inaccordance with this type of structure, a light emitting device in whichelements having different characteristics with respect to impurities arecombined, without mutual interference, can thus be completed.

What is claimed is:
 1. (canceled)
 2. A light emitting device comprising:a substrate; and a light emitting element comprising a light emittinglayer over the substrate, wherein the light emitting layer comprisesoxygen at a concentration equal to or less than 1×10¹⁹/cm³.
 3. The lightemitting device according to claim 2, wherein the substrate is anorganic resin substrate.
 4. The light emitting device according to claim3, wherein the organic resin substrate comprises any one of polyimide,polyethylene terephthalate, polyethylene naphthalene, polyether sulfone,and aramid.
 5. The light emitting device according to claim 2, whereinthe light emitting element further comprises: an anode between thesubstrate and the light emitting layer; and a cathode over the lightemitting layer.
 6. The light emitting device according to claim 2,wherein the light emitting device further comprises a transistorelectrically connected to the light emitting element.
 7. The lightemitting device according to claim 2, wherein the light emitting layercomprises an organic compound, and wherein the organic compound iscapable of obtaining light emission from a triplet excitation state. 8.A light emitting device comprising: a substrate; and a light emittingelement comprising a hole transporting layer over the substrate, whereinthe hole transporting layer comprises oxygen at a concentration equal toor less than 1×10¹⁹/cm³.
 9. The light emitting device according to claim8, wherein the substrate is an organic resin substrate.
 10. The lightemitting device according to claim 9, wherein the organic resinsubstrate comprises any one of polyimide, polyethylene terephthalate,polyethylene naphthalene, polyether sulfone, and aramid.
 11. The lightemitting device according to claim 8, wherein the light emitting elementfurther comprises: an anode between the substrate and the holetransporting layer; and a cathode over the hole transporting layer. 12.The light emitting device according to claim 8, wherein the lightemitting device further comprises a transistor electrically connected tothe light emitting element.
 13. The light emitting device according toclaim 8, wherein the hole transporting layer comprises aromaticamine-based material.
 14. A light emitting device comprising: aninsulating film; and a light emitting element comprising a lightemitting layer over the insulating film, wherein the light emittinglayer comprises oxygen at a concentration equal to or less than1×10¹⁹/cm³.
 15. The light emitting device according to claim 14, whereinthe insulating film is made from silicon oxide or silicon nitride. 16.The light emitting device according to claim 14, wherein the lightemitting element further comprises: an anode between the insulating filmand the light emitting layer; and a cathode over the light emittinglayer.
 17. The light emitting device according to claim 14, wherein thelight emitting device further comprises a transistor electricallyconnected to the light emitting element.
 18. The light emitting deviceaccording to claim 14, wherein the light emitting layer comprises anorganic compound, and wherein the organic compound is capable ofobtaining light emission from a triplet excitation state.
 19. A lightemitting device comprising: an insulating film; and a light emittingelement comprising a hole transporting layer over the insulating film,wherein the hole transporting layer comprises oxygen at a concentrationequal to or less than 1×10¹⁹/cm³.
 20. The light emitting deviceaccording to claim 19, wherein the insulating film is made from siliconoxide or silicon nitride.
 21. The light emitting device according toclaim 19, wherein the light emitting element further comprises: an anodebetween the insulating film and the hole transporting layer; and acathode over the hole transporting layer.
 22. The light emitting deviceaccording to claim 19, wherein the light emitting device furthercomprises a transistor electrically connected to the light emittingelement.
 23. The light emitting device according to claim 19, whereinthe hole transporting layer comprises aromatic amine-based material.